HP 866Mhz System Running Win ME Western Digital 40GB HDD Norton AV (w/ updated defs) Last night I ran a system scan and Norton found that the MBR had been modified. Not sure what caused this, but it repaired it and everything was fine. Restarted the computer, just fine. Today, something obviously happened again. Some wierd pop-up windows started coming up while I was disconnected from the internet. Figured it was a virus, ran Norton. No infected files, and MBR tested good. So I went into check MSCONFIG for any startup programs that might be causing it. Nothing there out of the ordinary. I hit okay, said offered to restart the computer, I did. Booting up gives me an "Invalid System Disk" error. Can't boot into windows at all. Can anybody offer some suggestions please, on how this could have happened, what I can do to recover it (if anything)?? Please! Why didn't Norton catch the problem? Any help is MUCH appreciated.